1. Field of the Invention
The invention relates to a hydrophobing agent for the treatment of a surface, in particular, of a nozzle ejection opening surface of a liquid-operating print head, comprising
a) chain, cross-linkable halogen-containing copolymers, PA1 b) cross-linkable agent, which engages in cross-linking bonds with the copolymers, and PA1 c) a solvent. PA1 a) chain-like, cross-linkable halogen-containing copolymers, PA1 b) a cross-linking agent entering into cross-linking bonds with the copolymers, PA1 c) a first solvent having a first boiling point, and PA1 d) a second solvent having a second boiling point deviating from the first boiling point of the first solvent, and wherein the weight components and boiling points of the solvents are determined such that the first solvent upon application on a surface to be coated is already substantially evaporated, whereas the second solvent evaporates substantially only after application accompanied by formation of a hydrophobically acting layer. The first solvent is substantially evaporated from the mixture during a path from an application apparatus to the surface to be coated. The mixture is applied to the surface to be coated. The coating is hardened on the surface by evaporation of the second solvent. An accelerator can be admixed to the mixture. The first solvent can be a tertiary butylacetate and the second solvent can be a .gamma.-butyrolactone.
2. Brief Description of the Background of the Invention Including Prior Art:
Hydrophobing agents provide and convey to the treated surface a repellent and dewetting effect both against aqueous as well as against organic solvents. Surfaces which are barely or not at all wettable by liquids can be desired in various fields of technology. In case of metallic surfaces, this can be required for the avoidance and elimination of corrosion. In connection with other objects, a wetting of the surface can be undesirable for technical reasons. For example, in case of print heads, the wetting behavior of the nozzle ejection opening surface in the area of the nozzle openings is of substantial importance for the achievable print quality.
A hydrophobing agent for the surface treatment, in particular for the nozzle ejection opening surface of an ink jet print head, is known in this context from the Printed European Patent Document WO 90/14958. The hydrophobing agent includes a silane as an active component, wherein an at least in part fluorinated organic group is bonded via a saturated radical to the silicon. This hydrophobing agent is liquid at room temperature and can be applied for example by dipping, by spraying, or by vapor deposition onto the surface to be treated. The application, however, has to be performed in a dry, absolutely water-free atmosphere. For this purpose, the hydrophobing agent is for example heated in a closed chamber comprising the body to be treated. The hydrophobing agent is in this case deposited onto the surfaces to be coated. The kind and the uniformity of the deposit determines directly the uniformity and stability of the formed hydrophobing agent layer.
A hydrophobing agent of the initially recited kind based on cross-linkable fluorine-containing copolymers is known from the Printed European Patent Document EP-B1-0,150,430. The copolymers are dissolved in an organic solvent, for example, an aliphatic alcohol or polyglycol. By addition of a cross-linking agent or hardener adhesion-stable, corrosion-resistant and weather-resistant, primers can be generated from these copolymers. A layer formed from these known hydrophobing agents exhibits however in case of mechanical load, for example a frequent wiping, only an insufficient long-term stability of the adhesion properties and can only insufficiently cover regions with insufficient partial adhesion. In addition, the known hydrophobing agent covers and coats dirt particles disposed on the surfaces only insufficiently such that these dirt particles can serve as a nuclei for an undesired liquid accumulation on the coated surface. A further problem of the known hydrophobing agent comprises that, in case of application from a vapor phase or by spraying onto the surface to be treated, there are generated islands, which are formed by an insufficient converging of the hydrophobing agent droplets deposited on the surface. This converging of the hydrophobing agent droplets is substantially dependent on the viscosity at the point in time of the application. The viscosity is essentially influenced by the original weight component part and the boiling point of the employed solvent as well as by the evaporation of the employed solvent caused by the application. At any rate, it is difficult with the known hydrophobing agent of the Printed European Patent Document EP-B1-0,150,430, to generate a uniform coating, since a relatively large solvent component allows in fact a good converging of the applied hydrophobing agent droplets, but that however, at the same time the applied hydrophobing agent, based on the high content in solvent, tends to an undesirable running off from the surface to be treated. A relative small solvent component at the time of application avoids in fact the undesired running off, however, this increases substantially the danger of the described formation of islands.